Shotcut video editor gets hardware accelerated color grading

If you've been wondering what video editor would get support for Movit's hardware-accelerated filters that we recently covered, we have the answer for you: it's Shotcut.

The editor, first introduced by Dan Dennedy last year, relies on MLT framework (also created by Dan). The work on the GLSL-based processing framework for MLT started about a year ago, but it was missing filters and color grading tools.

Fortunately, Steinar H. Gunderson came up with his Movit library last year, so now not only MLT can do GPU rendering, but also applies filters like the 3-way color grading tool here:

3-way color grading tool

All the supported filters work with 16-bit linear floating point precision per color channel. That's interesting too, because the topic of better-than-8bit precision caused a few drama threads in the Kdenlive's forum in the past.

Now, just how much difference does hardware acceleration make? Here's what Dan posted in the MLT's Google+ page recently:

For a friend, I just made a quick, informal comparison of traditional CPU-based image processing in MLT versus the new GLSL/GPU-based processing. I played a 720p24 clip upscaled to 1080p with Lanczos interpolation and applied a box blur. I had to use real_time=4 (4 image processing threads) to play this with melt without dropping frames, and it showed an average of 515% CPU utilization on a core i7 MacBook Pro. The same thing using the GLSL-based filters instead only required an average of 26% CPU utilization.

The most recent builds of Shotcut are shipping with blur, color grading, crop, glow, mirror, saturation and sharpen filters. There are some more Movit filters available that need a UI (e.g. white balance and vignette).

Has Movit become part of MLT then? Steinar says:

Movit will continue to be a separate project; I'm not involved in MLT as of right now.

Recent changes in upstream Movit include the switch to premultiplied alpha, a padding effect, various improvements in effects, optimizations of the effects chain, virtual output size in resizing effects, autoconf-based build system.

Since Kdenlive relies on MLT, is it going to make use of all this goodness?

As Dan stated, Kdenlive is still undertaking the massive refactoring, and there probably will be another maintenance release before the team will be able to switch to working on new features.

As for OpenShot, it's moving away from MLT towards its own library. However, no GPU-based processing has knowingly been proposed yet.

Nightly builds of Shotcut for Linux, Windows and OS X are available at shotcut.org. The next big feature that's likely to be worked on in Shotcut is properties animation.

7 Comments

Thank you for the coverage. You very accurately covered everything including the next steps. That really shows how much you are paying attention! Considering the range of topics that you cover here on LGW, it really says a lot about the integrity the journalism.

I should point out that additional Movit-based filters are used automatically “under-the-hood” such as color space conversion, scaling, and padding. It will be trivial to expose vignette. I will have to see about porting the Kdenlive color eyed-ropper widget before exposing white balance.